Chimacum,
WA, USA - After conducting a satisfactory pre-takeoff run-up check of
both the right magneto and left coil ignition system, the pilot departed
for his destination. Approximately 30 minutes into the flight the engine
began to run rough and the pilot determined that the right magneto was
not operating. He then selected the left ignition and, although the
engine initially continued to run roughly, eventually all power was
lost. The pilot selected an open field used by a farmer to operate his
Cessna 177 in and out of due to the non-availability of any other
adequate landing site. As he maneuvered through a 180 degree turn toward
the landing area, he noted a 1,000-foot/minute rate of descent, which
was greater than he had anticipated. The landing gear had been extended
and as the aircraft was maneuvered onto a short final, the right main
landing gear struck a cow. The aircraft yawed into a left skid,
contacted the ground and skidded through a barbwire fence. Post-crash
examination revealed that the right magneto had grounded internally
resulting in its failure to operate. Additional testing revealed the
left coil ignition system had also grounded internally as evidence by
arcing, and it too, had failed.

The National Transportation Safety Board determines the probable
cause(s) of this accident as follows:

An internal ground in the right magneto followed by an internal ground
evidenced by arcing in the left ignition coil unit, which led to failure
of both the right magneto and the left coil ignition system respectively
during cruise. Contributing factors were a cow impacted by the right
main landing gear and the pilot's unanticipated higher than expected
rate of descent during the 180 degree descending turn to final.